Q. 1. The Catholic Church's teaching on mandatory Sunday Mass, is that Biblical? I cannot find any reference to that question.
A. 1. One of the Ten Commandments states: “remember to keep holy the sabbath day. Six days you may labor and do all your work, but the seventh day is the sabbath of the Lord, your God. No work may be done then... in six days the Lord made the heavens and the earth, but on the seventh day He rested. That is why the Lord has blessed the Sabbath day and made it holy.” [Exodus 20:8-10]
Most likely you are going to say that the Commandments says nothing about going to Church. It simply commands that we set aside one day of the week as a day of rest, when no work is to be done.
As a result of this Commandment, it became customary among the Jewish people, however, to see the sabbath as a day to be “with” God in a special way. Much of their prayer centered in the home, but they also developed the custom of attending the synagogue on the Sabbath to hear and study the word of God. Their sabbath, or Seventh day, was on the day we call “Saturday.”
The “Holy Mass” had its beginning when early Christians gathered together in their homes to share a meal in memory of Jesus, as He had asked them to do on the night before he died - “The Last Supper” -. Originally, there was no obligation related to this. Christians got together to pray, the hear the Scriptures read, and to share the meal because they wanted to. Over time the meal became more formalized and ritualized, and included readings from Scripture. As more time passed and Christians became more and more distant from the time of Jesus their enthusiasm waned and they no longer gathered for Mass so eagerly. So the church imposed a rule making it mandatory that Christians attend Mass at least on Sunday. Sunday had become the day of worship, rather than the Jewish sabbath, because it was the day when Jesus rose from the dead. The obligation to attend Mass on Sunday is a Church law, not a Divine commandment like the 10 commandments.